The present invention relates to a method and an apparatus for reducing energy consumption when drying a paper web in a paper machine drying section, which web is formed on a fabric in the wire part of the paper machine, picked up from the fabric by pick-up means, and is thereafter conveyed to and through the drying section. The paper web is trimmed in the wire part of the machine by means of edge cutters so as to divide it into a trimmed web and couch trimmings while the web is being conveyed on a forming side of the fabric.
The paper web formed in the paper machine originally is of varying width and its edges are uneven with respect to straightness, thickness and grammage (basis weight). The finished paper web must be trimmed before reeling, and the widths of the edge portions cut away may be considerable due to the variation in width of the paper web. Furthermore, when manufacturing tissue, for example, the paper web also has to be slit into a plurality of webs of a predetermined width and wound again, which may cause additional waste.
The dried broke obtained when cutting the edge portions at a winder is very voluminous, which makes it difficult to collect and convey out of the way. This dried paper is slushed in water and recirculated to the paper manufacturing process. In light of the high energy costs which prevail today, the dried broke normally obtained during the manufacture of paper is a large problem.
It has been suggested, see U.S. Pat. No. 2,686,463 (Hornbostel) and U.S. Pat. No. 2,709,398 (Beachler), to reduce the energy consumed in the paper manufacturing process, primarily in the drying of the paper web, by trimming the web so that it is divided into a trimmed web and couch trimmings while it is being conveyed on the forming fabric, and picking up the trimmed web through the use of suction from the fabric for conveyance to and through the drying section, while attempting to avoid conveyance of the couch trimmings to the drying section.
It has been found, however, that the above earlier known technique is not effective when applied to paper grades of low grammage, such as tissue, because the couch trimmings have the tendency to adhere to the pick-up felt used for picking up the trimmed web and consequently the trimmings have had the tendency of accompanying the trimmed web to and through the drying section. The object of the present invention is to provide an improvement in this regard in that contact between the trimmings and the pickup felt is avoided.